Observed large-scale and deep-reaching compound ocean state changes over the past 60 years

Multiple climate-related stressors affect the ocean, including warming, acidification, deoxygenation and variations in salinity, with profound effects on Earth system cycles, marine ecosystems and human well-being. Nevertheless, a global perspective on the combined impacts of these changes on both surface and subsurface ocean conditions remains unclear. Here, applying a time-of-emergence methodology to observed physical and biogeochemical variables, collectively referred to as compound climatic impact-drivers, we show individual and compound ocean state changes have become increasingly prominent globally over the past 60 years. In particular, observations show the simultaneous emergence of compound climatic impact-drivers in regions spanning the subtropical and tropical Atlantic, the subtropical Pacific, the Arabian Sea and the Mediterranean Sea. We highlight extensive exposure of different ocean layers to compound emergence, characterized by significant intensity, duration and magnitude. These results provide a comprehensive framework and perspective to illustrate the ocean’s vulnerability to pervasive and interconnected changes in a warming climate.